Today, with an increasing demand for storing heat energy using inexpensive midnight electric power and taking out the stored heat energy during the day for hot-water supply, heating and other purposes, higher performance is required of heat storage apparatus.
Among various examples of conventionally-known heat storage apparatus is a heat-storage type heat exchanger apparatus disclosed, for example, in Japanese Patent Application Laid-open Publication No. HEI-11-264683 (hereinafter called “Patent Document 1”). FIG. 11 shows the heat-storage type heat exchanger apparatus disclosed in Patent Document 1, which includes a multiplicity of fluid passageways 3 (only one of which is shown in FIG. 11) each formed of ceramic wall sections 2a into a rectangular sectional shape. As a medium, such as air, is fed to the fluid passageways 3, the medium absorbs heat energy held by phase change materials 4. Specifically, as seen in FIG. 12, a heat storing body 1, generally in the form of a ceramic honeycomb structure 2, has, in addition to the fluid passageways 3, a multiplicity of chambers each having a rectangular sectional shape and accommodating the phase change material 4.
FIG. 13 is a fragmentary enlarged view of a circled portion 13 of FIG. 12, which particularly shows the above-mentioned phase-change-material accommodating chambers 101. In the figure, the chamber 101 is defined by partition wall sections 102, 103, 104 and 105, and the fluid passageway 3 is defined by partition wall sections 104, 106, 107 and 108.
To form the ceramic honeycomb structure 2 of FIG. 13, the ceramic material has to be subjected to various steps including component adjustment, powder-pressurizing molding, provisional burning and main burning, which would result in increased manufacturing costs. Metal extrusion molding might be among possible effective solutions for lowering the manufacturing costs; however, the metal extrusion molding would present the following problems.
FIG. 14 is explanatory of the problems presented by the technique disclosed in Patent Document 1. Mold 110 to be described below would be required in order to form, by extrusion molding, the phase-change-material accommodating chambers 101, fluid passageways 3 and partition wall sections 102–108. Namely, the mold 110 must have blocks 111 for forming the phase-change-material accommodating chambers 101, peripheral gaps 112, 113, 114 and 115 around the blocks 110, thin blocks 116 for forming the fluid passageways 3, peripheral gaps 114, 117, 118 and 119 around the thin blocks 110, and bridges 121 connecting and supporting the blocks 111 and 116.
Because a predetermined quantity of the phase change materials 4 must be retained in the apparatus, it is difficult to change the sectional area of the phase-change-material accommodating chambers 101 with a view to reducing the size and weight of the honeycomb structure 2. The sectional area of the fluid passageway 3, on the other hand, can be reduced if a flow rate of the fluid (heat exchanging medium) is increased. For example, doubling the fluid flow rate can halve a width (corresponding to a thickness t1 of the thin blocks 116) of the fluid passageways 3. The reduced width of the fluid passageways 3 can attain a reduced size of the honeycomb structure 2.
For reduction in the size of the honeycomb structure 2, the thickness t1 of the thin blocks 116 in FIG. 14 must be reduced in accordance with a desired reduced width of the fluid passageways 3. During the exclusion molding, a flowing metal material is interrupted by the blocks 111 and thin blocks 116 and thereby passes through the gaps 112–115 and 117–119, and such a flow of the metal material would produce a force operating on the blocks 111 and 116 in a direction perpendicular to the sheet of the figure.
If the thickness of the thin blocks 116 is reduced below a given value, the thin blocks 116 would lack rigidity and thus undesirably deform due to the above-mentioned operating force. In addition, only thin bridges 121 can be provided for the thin blocks 116, so that the blocks 116 can not be supported sufficiently by the thin bridges 121. Therefore, with the extrusion molding, it is difficult to reduce the width (t1) of the fluid passageways 3.
The increased sectional area of the fluid passageways 3 increases the amount of the fluid staying within the heat storage apparatus, which results in increased volume and weight of the apparatus and increased heat mass of the fluid. To compensate for the increased volume, weight and heat mass, extra heat energy would be required, so that heat energy tends to run short during a heat release operation by the apparatus.
Thus, there has been a demand for a more sophisticated technique which permits use of metal extrusion molding and yet can reduce the width of the fluid passageways.